18F-Fluoroestradiol Tumor Uptake Is Heterogeneous and Influenced by Site of Metastasis in Breast Cancer Patients

Predictive and prognostic value of 18F-FES PET/CT for patients with recurrent or metastatic breast cancer treated with endocrine therapy plus cyclin-dependent kinase 4/6 inhibitors

PURPOSE

Estrogen receptor (ER) expression and heterogeneity affect endocrine therapy efficacy. 18F-fluoroestradiol (18F-FES) PET/CT is an effective non-invasive method to analyze systemic ER expression. This study aimed to examine the predictive/prognostic value of 18F-FES PET/CT for patients treated with endocrine therapy plus cyclin-dependent kinase 4/6 (CDK4/6) inhibitors.

METHODS

Patients were identified from a prospective cohort for post-marketing surveillance of 18F-FES enrolled between April 2021 and April 2023 at Asan Medical Center. In this retrospective analysis, patients with ER-positive, HER2-negative recurrent/metastatic breast cancer who underwent CDK4/6 inhibitor-based endocrine therapy and pre-treatment 18F-FES PET/CT were included.

RESULTS

A total of 127 women were included. The endocrine therapy used was aromatase inhibitors in 96 patients (76%) and fulvestrant in 31 patients (24%). There were 25 (20%) and 102 (80%) patients in the "with FES-negative" (3 completely negative, 22 mixed) and "FES-positive" groups, respectively. 18F-FES status correlated with progression-free survival (PFS) following endocrine therapy with CDK4/6 inhibitors and overall survival (OS) ("with FES-negative" group: hazard ratio for PFS, 3.9, p < 0.001; for OS, 3.7, p = 0.008). Reduced benefit from endocrine treatment in the "with FES-negative" group was consistent across subgroups including menopausal status, endocrine sensitivity, and treatment regimen.

CONCLUSION

ER expression determined by 18F-FES PET/CT predicted the efficacy of CDK4/6 inhibitor-based endocrine therapy and was prognostic for survival in recurrent/metastatic ER-positive, HER2-negative breast cancer.

[18F]F-FES PET for diagnosis, staging, and endocrine therapy prediction in ER-positive breast cancer: a systematic review and meta-analysis

BACKGROUND

This meta-analysis evaluates the diagnostic and staging accuracy of [18F]F-FES PET/CT, its ability to detect estrogen receptor (ER) positivity, and its effectiveness in predicting response to endocrine therapy in ER-positive (ER+) breast cancer. A systematic search of PubMed, Embase (OVID), and Web of Science databases was conducted for studies published between 2013 and June 2024. Studies involving ER + breast cancer patients who underwent [18F]F-FES PET/CT were included. We analyzed the diagnostic accuracy, ER detection capability, and predictive ability for endocrine therapy response.

RESULTS

Out of 189 studies initially identified, 21 met the inclusion criteria. For diagnosis and staging compared to [18F]F-FDG PET (10 studies), [18F]F-FES PET/CT demonstrated a sensitivity of 0.75 (95% CI: 0.62-0.85) and a false positive rate (FPR) of 0.27 (95% CI: 0.09-0.50). For ER detection (7 studies), sensitivity was 0.86 (95% CI: 0.71-0.94) with an FPR of 0.45 (95% CI: 0.19-0.73). For predicting response to endocrine therapy (12 studies), [18F]F-FES PET/CT showed a sensitivity of 0.79 (95% CI: 0.62-0.89) and an FPR of 0.58 (95% CI: 0.42-0.72).

CONCLUSIONS

[18F]F-FES PET/CT is valuable for diagnosing and staging ER + breast cancer, assessing ER status, and predicting response to endocrine therapy. Its implementation can improve treatment planning and patient outcomes in breast cancer management.

Diagnostic Accuracy of 18 F-FES PET/CT for the Detection of Recurrent and Metastatic Breast Cancer

PURPOSE

To evaluate the diagnostic value of 16α- 18 F-fluoro-17β-fluoroestradiol ( 18 F-FES) PET/CT for distant metastasis or recurrence in patients with estrogen receptor (ER)-positive breast cancer.

METHODS

Patients with ER-positive breast cancer and suspected of de novo metastasis or recurrence were retrospectively identified from a prospective cohort enrolled for a postmarketing surveillance study of 18 F-FES at our institution. Per-patient diagnostic accuracy was assessed using pathology or 2 or more standard-of-care imaging procedures with a minimum of 6 months of follow-up as the reference standard. The per-region detection rate of 18 F-FES PET/CT was evaluated and compared with that of standard-of-care imaging.

RESULTS

Of the 162 included patients, 104 and 58 were suspected to have recurrence or de novo metastasis, respectively. The overall sensitivity and specificity of 18 F-FES PET/CT were 95% (95% confidence interval [CI], 89%-98%) and 89% (95% CI, 76%-96%), respectively. When stratified according to clinical settings, the sensitivity and specificity were 95% (95% CI, 88%-99%) and 96% (95% CI, 78%-100%), respectively, for detecting recurrence, and 94% (95% CI, 81%-99%) and 82% (95% CI, 60%-95%) for detecting distant metastasis. In region-based analysis, the overall detection rate of 18 F-FES PET/CT was significantly higher than that of standard-of-care imaging (92% [95% CI, 89%-94%] vs 83% [95% CI, 79%-87%], P < 0.001).

CONCLUSIONS

18 F-FES PET/CT showed excellent diagnostic performance in patients with ER-positive breast cancer suspected of de novo metastasis or recurrence.

Navigating the biophysical landscape: how physical cues steer the journey of bone metastatic tumor cells

Many tumors prefer to metastasize to bone, but the underlying mechanisms remain elusive. The human skeletal system has unique physical properties, that are distinct from other organs, which play a key role in directing the behavior of tumor cells within bone. Understanding the physical journey of tumor cells within bone is crucial. In this review we discuss bone metastasis in the context of how physical cues in the bone vasculature and bone marrow niche regulate the fate of tumor cells. Our objective is to inspire innovative diagnostic and therapeutic approaches for bone metastasis from a mechanobiological perspective.

Molecular Imaging of Steroid Receptors in Breast Cancer

ABSTRACT

Steroid receptors regulate gene expression for many important physiologic functions and pathologic processes. Receptors for estrogen, progesterone, and androgen have been extensively studied in breast cancer, and their expression provides prognostic information as well as targets for therapy. Noninvasive imaging utilizing positron emission tomography and radiolabeled ligands targeting these receptors can provide valuable insight into predicting treatment efficacy, staging whole-body disease burden, and identifying heterogeneity in receptor expression across different metastatic sites. This review provides an overview of steroid receptor imaging with a focus on breast cancer and radioligands for estrogen, progesterone, and androgen receptors.

Bone Metastases

ABSTRACT

Bone metastases occur frequently in common malignancies such as breast and prostate cancer. They are responsible for considerable morbidity and skeletal-related events. Fortunately, there are now several systemic, focal, and targeted therapies that can improve quality and length of life, including radionuclide therapies. It is therefore important that bone metastases can be detected as early as possible and that treatment can be accurately and sensitively monitored. Several bone-specific and tumor-specific single-photon emission computed tomography and positron emission tomography molecular imaging agents are available, for detection and monitoring response to systemic therapeutics, as well as theranostic agents to confirm target expression and predict response to radionuclide therapies.

Can 18F-FES PET Improve the Evaluation of 18F-FDG PET in Patients With Metastatic Invasive Lobular Carcinoma?

PURPOSE

Invasive lobular carcinoma (ILC) exhibits a low affinity for 18F-FDG. The estrogen receptor (ER) is commonly expressed in ILCs, suggesting a potential benefit of targeting with the ER probe 18F-FES in this patient population. The objective of this study was to evaluate the diagnostic performance of 18F-FES imaging in patients with metastatic ILC and compare it with that of 18F-FDG.

METHODS

We conducted a retrospective analysis of 20 ILC patients who underwent concurrent 18F-FES and 18F-FDG PET/CT examinations in our center. 18F-FES and 18F-FDG imaging were analyzed to determine the total count of tracer-avid lesions in nonbone sites and their corresponding organ systems, assess the extent of anatomical regions involved in bone metastases, and measure the SUVmax values for both tracers.

RESULTS

Among 20 ILC patients, 65 nonbone lesions were found to be distributed in 13 patients, and 16 patients were diagnosed with bone metastasis, which was distributed in 54 skeletal anatomical regions. The detection rate of 18F-FDG in nonbone lesions was higher than that of 18F-FES (57 vs 37, P < 0.001). 18F-FES demonstrated a superior ability to detect nonbone lesions in 4 patients, whereas 18F-FDG was superior in 5 patients (P > 0.05). Among 9/16 patients with bone metastasis, 18F-FES demonstrated a significant advantage in the detection of bone lesions compared with 18F-FDG (P = 0.05). Furthermore, patients with only 18F-FES-positive lesions (12/12) were administered endocrine regimens, whereas patients lacking 18F-FES uptake (2/3) predominantly received chemotherapy.

CONCLUSIONS

18F-FES is more effective than 18F-FDG in detecting bone metastasis in ILC, but it does not demonstrate a significant advantage in nonbone lesions. Additionally, the results of examination with 18F-FES have the potential to guide patient treatment plans.

Dynamic whole-body [18F]FES PET/CT increases lesion visibility in patients with metastatic breast cancer

BACKGROUND

Correct classification of estrogen receptor (ER) status is essential for prognosis and treatment planning in patients with breast cancer (BC). Therefore, it is recommended to sample tumor tissue from an accessible metastasis. However, ER expression can show intra- and intertumoral heterogeneity. 16α-[18F]fluoroestradiol ([18F]FES) Positron Emission Tomography/Computed Tomography (PET/CT) allows noninvasive whole-body (WB) identification of ER distribution and is usually performed as a single static image 60 min after radiotracer injection. Using dynamic whole-body (D-WB) PET imaging, we examine [18F]FES kinetics and explore whether Patlak parametric images ( K i ) are quantitative and improve lesion visibility.

RESULTS

This prospective study included eight patients with metastatic ER-positive BC scanned using a D-WB PET acquisition protocol. The kinetics of [18F]FES were best characterized by the irreversible two-tissue compartment model in tumor lesions and in the majority of organ tissues. K i values from Patlak parametric images correlated with K i values from the full kinetic analysis, r2 = 0.77, and with the semiquantitative mean standardized uptake value (SUVmean), r2 = 0.91. Furthermore, parametric K i images had the highest target-to-background ratio (TBR) in 162/164 metastatic lesions and the highest contrast-to-noise ratio (CNR) in 99/164 lesions compared to conventional SUV images. TBR was 2.45 (95% confidence interval (CI): 2.25-2.68) and CNR 1.17 (95% CI: 1.08-1.26) times higher in K i images compared to SUV images. These quantitative differences were seen as reduced background activity in the K i images.

CONCLUSION

[18F]FES uptake is best described by an irreversible two-tissue compartment model. D-WB [18F]FES PET/CT scans can be used for direct reconstruction of parametric K i images, with superior lesion visibility and K i values comparable to K i values found from full kinetic analyses. This may aid correct ER classification and treatment decisions. Trial registration ClinicalTrials.gov: NCT04150731, https://clinicaltrials.gov/study/NCT04150731.

ER status conversion and subsequent treatment: an assessment of negative ER expression detected by 18F-FES PET in metastatic breast cancer patients with ER-positive primary tumors

Background

The 18F-fluoroestradiol positron emission tomography/computed tomography (18F-FES PET/CT) technique provides a convenient method to evaluate the overall estrogen receptor (ER) expression in metastatic breast cancer (MBC) patients. There are long debates on the characteristics and treatment strategy of patients with positive primary ER lesions but negative ER expression in metastatic disease. 18F-FES PET offers an opportunity to answer this question.

Objectives

This study aimed to characterize the primary ER-positive patients with advanced-stage FES negativity and investigate the real-world treatment decisions made by physicians subsequently, and compare the efficacy between different regimens.

Design

This observational cohort study was conducted at Fudan University Shanghai Cancer Center, enrolling breast cancer patients with ER-positive primary tumors who showed advanced-stage FES negativity.

Methods

Descriptive statistics were used in clinicopathologic characteristics and compared with a chi-square test or t-test. In addition, progression-free survival (PFS) was estimated by the Kaplan-Meier method and compared by log-rank test.

Results

16.6% (52/314) of patients with an ER-positive primary tumor had negative ER expression assessed by 18F-FES for MBC prior to receiving first-line systemic therapy, among whom adjuvant endocrine therapy was prevalently utilized (86.5%, 45/52). The rate of FES negativity in the advanced stage was negatively correlated with levels of ER expression of primary tumors. Chemotherapy (83.3%, 40/48) was the most common treatment strategy afterward, among which capecitabine monotherapy (62.5%, 25/40) was a dominant alternative. PFS was significantly prolonged with capecitabine alone versus other chemotherapy (median PFS: 13.14 versus 6.21 months, p = 0.029).

Conclusion

Negative conversion of ER in MBC detected by 18F-FES occurred frequently. Patients with lower ER expression in the primary lesion were more likely to have negative ER expression in the metastasis. In real-world clinical practice, most physicians primarily opted for chemotherapy, with capecitabine monotherapy being a commonly selected regimen.

Trial registration

ClinicalTrials.gov identifier: NCT05797987.

18F-FES and 18F-FDG PET/CT imaging as a predictive biomarkers for metastatic breast cancer patients undergoing cyclin-dependent 4/6 kinase inhibitors with endocrine treatment

OBJECTIVE

The aim of this study was to investigate the potential value of dual tracers 18F-FDG and 18F-FES PET/CT in predicting response to Cyclin-Dependent 4/6 Kinase (CDK4/6) inhibitors combined with endocrine therapy for metastatic estrogen receptor (ER)-positive breast cancer patients.

METHODS

This retrospective study enrolled 38 ER-positive metastatic breast cancer patients from our center who underwent both 18F-FDG and 18F-FES PET/CT scans within 1 month before CDK4/6 inhibitors combined with endocrine therapy. The extracted parameters comprised the maximum standardized uptake value (SUVmax) for both FDG and FES PET, as well as the ratio between FES and FDG SUVmax. Each parameter was dichotomized based on its median threshold. The primary endpoint was progression-free survival (PFS), which was estimated using the Kaplan-Meier method and compared by the log-rank test.

RESULTS

After a median follow-up of 15.6 months, progressive disease was observed in 23 out of 38 patients, and the median PFS for the whole cohort was 21.0 months [95% confidence interval (CI) 12.7-29.3]. FES and FDG PET identified 6 patients (15.8%) with FES-negative lesions, suggesting ER heterogeneity in metastatic lesions. The median PFS of these patients was only 5.3 months (95% CI 1.7-8.9), which was substantially shorter than that of patients with 100% FES-positive lesions (median PFS 22.9 months, 95% CI 17.1-28.7, P < 0.001). Patients with 100% FES-positive lesions who had high FES/FDG showed significantly shorter PFS compared to those with low FES/FDG (14.9 vs. 30.5 months, P = 0.003).

CONCLUSIONS

This study shows that FDG and FES PET imaging may serve as valuable tools for patient selection in the context of CDK4/6 inhibitor therapy combined with endocrine treatment, and have the potential to function as prognostic biomarkers.

The Application of 18F-FES PET in Clinical Cancer Care: A Systematic Review

INTRODUCTION

[18F]fluoroestradiol (FES) can be used for the noninvasive visualization and quantification of tumor estrogen receptor (ER) expression and activity and was FDA-approved as a diagnostic agent in May 2022 for detecting ER-positive lesions in patients with recurrent or metastatic breast cancer. PET imaging was also used to detect ER-positive lesions and malignancy among patients with uterine, ovarian, and other ER-positive solid tumors. We conducted a systemic review of the studies on FES PET imaging used among patients with cancer not limited to breast cancer to better understand the application of FES PET imaging.

METHODS

PubMed/MEDLINE and Cochrane Library databases were used to perform a comprehensive and systematic search and were updated until August 15, 2022. Two authors independently reviewed the titles and abstracts of the retrieved articles by using the search algorithm and selected the articles based on the inclusion and exclusion criteria. All statistical analyses were conducted using R statistical software.

RESULTS

Forty-three studies with 2352 patients were included in the qualitative synthesis, and 23 studies with 1388 patients were included in the quantitative analysis, which estimated the FES-positive detection rate. Thirty-two studies (77%) included breast cancer patients in 43 included studies. The FES SUVmean was higher in patients with endometrial cancer (3.4-5.3) than in those with breast cancer (2.05) and uterine sarcoma (1.1-2.6). The pooled detection rates of FES PET imaging were 0.80 for breast and 0.84 for ovarian cancer patients, both similar to that of 18F-FDG. The FES uptake threshold of 1.1 to 1.82 could detect 11.1% to 45% ER heterogeneity, but the threshold of FES uptake did not have consistent predictive ability for prognosis among patients with breast cancer, unlike uterine cancer. However, FES uptake can effectively predict and monitor treatment response, especially endocrine therapy such as estradiol, ER-blocking agents (fulvestrant and tamifoxen), and aromatase inhibitors (such as letrozole and Z-endoxifen).

CONCLUSIONS

[18F]fluoroestradiol PET is not only a convenient and accurate diagnostic imaging tool for detecting ER-expressing lesions in patients with breast and ovarian cancer but also among patients with uterine cancer. [18F]fluoroestradiol PET is a noninvasive predictive and monitoring tool for treatment response and prognosis.

Summary: Appropriate Use Criteria for Estrogen Receptor-Targeted PET Imaging with 16α-18F-Fluoro-17β-Fluoroestradiol

PET imaging with 16α-¹⁸F-fluoro-17β-fluoroestradiol (¹⁸F-FES), a radiolabeled form of estradiol, allows whole-body, noninvasive evaluation of estrogen receptor (ER). ¹⁸F-FES is approved by the U.S. Food and Drug Administration as a diagnostic agent "for the detection of ER-positive lesions as an adjunct to biopsy in patients with recurrent or metastatic breast cancer." The Society of Nuclear Medicine and Molecular Imaging (SNMMI) convened an expert work group to comprehensively review the published literature for ¹⁸F-FES PET in patients with ER-positive breast cancer and to establish appropriate use criteria (AUC). The findings and discussions of the SNMMI ¹⁸F-FES work group, including example clinical scenarios, were published in full in 2022 and are available at https://www.snmmi.org/auc Of the clinical scenarios evaluated, the work group concluded that the most appropriate uses of ¹⁸F-FES PET are to assess ER functionality when endocrine therapy is considered either at initial diagnosis of metastatic breast cancer or after progression of disease on endocrine therapy, the ER status of lesions that are difficult or dangerous to biopsy, and the ER status of lesions when other tests are inconclusive. These AUC are intended to enable appropriate clinical use of ¹⁸F-FES PET, more efficient approval of FES use by payers, and promotion of investigation into areas requiring further research. This summary includes the rationale, methodology, and main findings of the work group and refers the reader to the complete AUC document.

To Identify Small Bowel Metastasis From Lobular Breast Cancer on 18 F-Fluoroestradiol PET/CT : Necessary to Adjust the Background Uptake Level

ABSTRACT

A 61-year-old woman was incidentally found to have small bowel metastasis from an undiagnosed lobular breast cancer in a workup for her acute presentation of small bowel obstruction. However, outside-hospital mammogram and breast ultrasound failed to reveal primary breast cancer. At 3.5 months postsurgery, the patient transferred her care to our hospital and received initial staging 18 F-fluoroestradiol (FES) PET/CT. The occult primary right breast cancer and previously biopsied right axilla lymph node were visualized on FES PET/CT. The intense small bowel uptake of FES was initially considered as physiological; however, after readjusting the background FES level on PET, an intense focus at small bowel anastomosis site became obvious.

Nuclear Receptor Imaging In Vivo-Clinical and Research Advances

Nuclear receptors are transcription factors that function in normal physiology and play important roles in diseases such as cancer, inflammation, and diabetes. Noninvasive imaging of nuclear receptors can be achieved using radiolabeled ligands and positron emission tomography (PET). This quantitative imaging approach can be viewed as an in vivo equivalent of the classic radioligand binding assay. A main clinical application of nuclear receptor imaging in oncology is to identify metastatic sites expressing nuclear receptors that are targets for approved drug therapies and are capable of binding ligands to improve treatment decision-making. Research applications of nuclear receptor imaging include novel synthetic ligand and drug development by quantifying target drug engagement with the receptor for optimal therapeutic drug dosing and for fundamental research into nuclear receptor function in cells and animal models. This mini-review provides an overview of PET imaging of nuclear receptors with a focus on radioligands for estrogen receptor, progesterone receptor, and androgen receptor and their use in breast and prostate cancer.

Imaging of Bone Metastases in Breast Cancer

Bone metastases are a common site of spread in advanced breast cancer and responsible for morbidity and high health care costs. Imaging contributes to staging and response assessment of the skeleton and has been instrumental in guiding patient management for several decades. Historically this has been with radiographs, computed tomography and bone scans. More recently, molecular and hybrid imaging methods have undergone significant development, including the addition of single photon emission computed tomography/computed tomography to the bone scan, positron emission tomography, with bone-specific and tumor-specific tracers, and magnetic resonance imaging with complementary functional diffusion-weighted imaging. These have allowed different aspects of the abnormal biology associated with bone metastases to be explored. There is ability to interrogate the bone microenvironment with bone-specific tracers and cancer cell characteristics with tumor-specific methods that complement morphological appearances on computed tomography or magnetic resonance imaging. Alongside the advent of novel, more effective and nuanced therapies for bone metastases in breast cancer, there is accumulating evidence that the developments in imaging allow more sensitive and specific detection of bone metastases as well as more accurate and earlier assessment of treatment response leading to improvements in patient management.

Molecular Imaging Assessment of Hormonally Sensitive Breast Cancer: An Appraisal of 2-[18F]-Fluoro-2-Deoxy-Glucose and Newer Non-2-[18F]-Fluoro-2-Deoxy-Glucose PET Tracers

Hormone-sensitive breast cancer, which demonstrates hormone receptor positivity, accounts for approximately 75% of newly diagnosed breast cancer. 2-[18F]-Fluoro-2-deoxy-glucose is the nonspecific radiotracer of glucose metabolism as opposed to specific receptor based tracers like 16α-[18F]-fluoro-17β-estradiol and [18F]-fluoro-furanyl-norprogesterone, which provide essential information about receptor status in the management of hormonally active malignancies. The complementary information provided by (a) 2-[18F]-fluoro-2-deoxy-glucose imaging for staging and prognostication along with (b) analyzing the hormonal receptor status with receptor-based PET imaging in breast cancer can optimize tumor characterization and influence patient management.

PET-CT in Clinical Adult Oncology: II. Primary Thoracic and Breast Malignancies

Simple Summary

Positron emission tomography (PET), typically combined with computed tomography (CT), has become a critical advanced imaging technique in oncology. With PET-CT, a radioactive molecule (radiotracer) is injected in the bloodstream and localizes to sites of tumor because of specific cellular features of the tumor that accumulate the targeting radiotracer. The CT scan, performed at the same time, provides information to facilitate assessment of the amount of radioactivity from deep or dense structures, and to provide detailed anatomic information. PET-CT has a variety of applications in oncology, including staging, therapeutic response assessment, restaging, and surveillance. This series of six review articles provides an overview of the value, applications, and imaging and interpretive strategies of PET-CT in the more common adult malignancies. The second article in this series addresses the use of PET-CT in breast cancer and other primary thoracic malignancies.

Abstract

Positron emission tomography combined with x-ray computed tomography (PET-CT) is an advanced imaging modality with oncologic applications that include staging, therapy assessment, restaging, and surveillance. This six-part series of review articles provides practical information to providers and imaging professionals regarding the best use of PET-CT for the more common adult malignancies. The second article of this series addresses primary thoracic malignancy and breast cancer. For primary thoracic malignancy, the focus will be on lung cancer, malignant pleural mesothelioma, thymoma, and thymic carcinoma, with an emphasis on the use of FDG PET-CT. For breast cancer, the various histologic subtypes will be addressed, and will include ¹⁸F fluorodeoxyglucose (FDG), recently Food and Drug Administration (FDA)-approved ¹⁸F-fluoroestradiol (FES), and ¹⁸F sodium fluoride (NaF). The pitfalls and nuances of PET-CT in breast and primary thoracic malignancies and the imaging features that distinguish between subcategories of these tumors are addressed. This review will serve as a resource for the appropriate roles and limitations of PET-CT in the clinical management of patients with breast and primary thoracic malignancies for healthcare professionals caring for adult patients with these cancers. It also serves as a practical guide for imaging providers, including radiologists, nuclear medicine physicians, and their trainees.

Clinical Validity of 16α-[18F]Fluoro-17β-Estradiol Positron Emission Tomography/Computed Tomography to Assess Estrogen Receptor Status in Newly Diagnosed Metastatic Breast Cancer

PURPOSE

Determining the estrogen receptor (ER) status is essential in metastatic breast cancer (MBC) management. Whole-body ER imaging with 16α-[¹⁸F]fluoro-17β-estradiol positron emission tomography ([¹⁸F]FES-PET) is increasingly used for this purpose. To establish the clinical validity of the [¹⁸F]FES-PET, we studied the diagnostic accuracy of qualitative and quantitative [¹⁸F]FES-PET assessment to predict ER expression by immunohistochemistry in a metastasis.

METHODS

In a prospective multicenter trial, 200 patients with newly diagnosed MBC underwent extensive workup including molecular imaging. For this subanalysis, ER expression in the biopsied metastasis was related to qualitative whole-body [¹⁸F]FES-PET evaluation and quantitative [¹⁸F]FES uptake in the corresponding metastasis. A review and meta-analysis regarding [¹⁸F]FES-PET diagnostic performance were performed.

RESULTS

Whole-body [¹⁸F]FES-PET assessment predicted ER expression in the biopsied metastasis with good accuracy: a sensitivity of 95% (95% CI, 89 to 97), a specificity of 80% (66 to 89), a positive predictive value (PPV) of 93% (87 to 96), and a negative predictive value (NPV) of 85% (72 to 92) in 181 of 200 evaluable patients. Quantitative [¹⁸F]FES uptake predicted ER immunohistochemistry in the corresponding metastasis with a sensitivity/specificity of 91%/69% and a PPV/NPV of 90%/71% in 156 of 200 evaluable patients. For bone metastases, PPV/NPV was 92%/81%. Meta-analysis with addition of our data has increased diagnostic performance and narrowed the 95% CIs compared with previous studies with a sensitivity/specificity of both 86% (81 to 90 and 73 to 93, respectively).

CONCLUSION

In this largest prospective series so far, we established the clinical validity of [¹⁸F]FES-PET to determine tumor ER status in MBC. In view of the high diagnostic accuracy of qualitatively assessed whole-body [¹⁸F]FES-PET, this noninvasive imaging modality can be considered a valid alternative to a biopsy of a metastasis to determine ER status in newly MBC (ClinicalTrials.gov identifier: NCT01957332).

Clinical Evaluation of Nuclear Imaging Agents in Breast Cancer

Precision medicine is the customization of therapy for specific groups of patients using genetic or molecular profiling. Noninvasive imaging is one strategy for molecular profiling and is the focus of this review. The combination of imaging and therapy for precision medicine gave rise to the field of theranostics. In breast cancer, the detection and quantification of therapeutic targets can help assess their heterogeneity, especially in metastatic disease, and may help guide clinical decisions for targeted treatments. Positron emission tomography (PET) or single-photon emission tomography (SPECT) imaging has the potential to play an important role in the molecular profiling of therapeutic targets in vivo for the selection of patients who are likely to respond to corresponding targeted therapy. In this review, we discuss the state-of-the-art nuclear imaging agents in clinical research for breast cancer. We reviewed 17 clinical studies on PET or SPECT agents that target 10 different receptors in breast cancer. We also discuss the limitations of the study designs and of the imaging agents in these studies. Finally, we offer our perspective on which imaging agents have the highest potential to be used in clinical practice in the future.

Head-to-Head Comparison between 18F-FES PET/CT and 18F-FDG PET/CT in Oestrogen Receptor-Positive Breast Cancer: A Systematic Review and Meta-Analysis

¹⁸F-FDG PET/CT is a powerful diagnostic tool in breast cancer (BC). However, it might have a reduced sensitivity in differentiated, oestrogen receptor-positive (ER+) BC. In this setting, specific molecular imaging with fluorine-oestradiol (¹⁸F-FES) PET/CT could help in overcoming these limitations; however, the literature on the diagnostic accuracy of this method is limited. We therefore planned this systematic review and meta-analysis to compare ¹⁸F-FDG and ¹⁸F-FES PET/CT in ER+ BC patients. We performed a literature search to identify all studies performing a head-to-head comparison between the two methods; we excluded review articles, preclinical studies, case reports and small case series. Finally, seven studies were identified (overall: 171 patients; range: 7–49 patients). A patients-based analysis (PBA) showed that ¹⁸F-FDG and ¹⁸F-FES PET/CT had a similar high pooled sensitivity (97% and 94%, respectively) at the lesion-based analysis (LBA), ¹⁸F-FES performed slightly better than ¹⁸F-FDG (pooled sensitivity: 95% vs. 85%, respectively). Moreover, when we considered only the studies dealing with the restaging setting (n = 3), this difference in sensitivity was even more marked (98% vs. 81%, respectively). In conclusion, both tracers feature an excellent sensitivity in ER+ BC; however, ¹⁸F-FES PET/CT could be preferred in the restaging setting.

Analyzing the Estrogen Receptor Status of Liver Metastases with [18F]-FES-PET in Patients with Breast Cancer

Background: Positron emission tomography (PET) with 16α-[¹⁸F]-fluoro-17β-estradiol ([¹⁸F]-FES) can visualize estrogen receptor (ER) expression, but it is challenging to determine the ER status of liver metastases, due to high physiological [¹⁸F]-FES uptake. We evaluated whether [¹⁸F]-FES-PET can be used to determine the ER status of liver metastases, using corresponding liver biopsies as the gold standard. Methods: Patients with metastatic breast cancer (n = 23) were included if they had undergone a [¹⁸F]-FES-PET, liver metastasis biopsy, CT-scan, and [¹⁸F]-FDG-PET. [¹⁸F]-FES-PET scans were assessed by visual and quantitative analysis, tracer uptake was correlated with ER expression measured by immunohistochemical staining and the effects of region-of-interest size and background correction were determined. Results: Visual analysis allowed ER assessment of liver metastases with 100% specificity and 18% sensitivity. Quantitative analysis improved the sensitivity. Reduction of the region-of-interest size did not further improve the results, but background correction improved ER assessment, resulting in 83% specificity and 77% sensitivity. Using separate thresholds for ER+ and ER− metastases, positive and negative predictive values of 100% and 75%, respectively, could be obtained, although 30% of metastases remained inconclusive. Conclusion: In the majority of liver metastases, ER status can be determined with [¹⁸F]-FES-PET if background correction and separate thresholds are applied.

Value of 18F-FES PET in Solving Clinical Dilemmas in Breast Cancer Patients: A Retrospective Study

Breast cancer (BC) is a heterogeneous disease in which estrogen receptor (ER) expression plays an important role in most tumors. A clinical dilemma may arise when a metastasis biopsy to determine the ER status cannot be performed safely or when ER heterogeneity is suspected between tumor lesions. Whole-body ER imaging, such as 16α-18F-fluoro-17β-estradiol (18F-FES) PET, may have added value in these situations. However, the role of this imaging technique in routine clinical practice remains to be further determined. Therefore, we assessed whether the physician's remaining clinical dilemma after the standard workup was solved by the 18F-FES PET scan. Methods: This retrospective study included 18F-FES PET scans of patients who had (or were suspected to have) ER-positive metastatic BC and for whom a clinical dilemma remained after the standard workup. The scans were performed at the University Medical Center of Groningen between November 2009 and January 2019. We investigated whether the physician's clinical dilemma was solved, defined either as solving the clinical dilemma through the 18F-FES PET results or as basing a treatment decision directly on the 18F-FES PET results. In addition, the category of the clinical dilemma was reported, as well as the rate of 18F-FES-positive or -negative PET scans, and any correlation to the frequency of solved dilemmas was determined. Results: One hundred 18F-FES PET scans were performed on 83 patients. The clinical dilemma categories were inability to determine the extent of metastatic disease or suspected metastatic disease with the standard workup (n = 52), unclear ER status of the tumor (n = 31), and inability to determine which primary tumor caused the metastases (n = 17). The dilemmas were solved by 18F-FES PET in 87 of 100 scans (87%). In 81 of 87 scans, a treatment decision was based directly on 18F-FES PET results (treatment change, 51 scans; continuance, 30 scans). The frequency of solved dilemmas was not related to the clinical dilemma category (P = 0.334). However, the frequency of solved dilemmas was related to whether scans were 18F-FES-positive (n = 63) or 18F-FES-negative (n = 37; P < 0.001). Conclusion: For various indications, the 18F-FES PET scan can help to solve most clinical dilemmas that may remain after the standard workup. Therefore, the 18F-FES PET scan has added value in BC patients who present the physician with a clinical dilemma.

Heterogeneity of bone metastases as an important prognostic factor in patients affected by oestrogen receptor-positive breast cancer. The role of combined [18F]Fluoroestradiol PET/CT and [18F]Fluorodeoxyglucose PET/CT

PURPOSE

To assess the prognostic role of different inter and intralesional expression (heterogeneity) of oestrogen receptor (ER) in bone metastases, as identified by the combined use of [18F]FES PET/CT and [18F]FDG PET/CT in patients with oestrogen receptor-positive (ER+) metastatic breast cancer (BC).

METHODS

We analysed patients with a new diagnosis of bone metastases who were candidates for first-line systemic endocrine therapy. Before starting therapy, patients underwent baseline [18F]FES PET/CT and [18]FDG PET/CT. Semi-quantitative evaluation of whole-body bone metabolic burden (WB-B-MB) was performed on [18F]FES and [18F]FDG PET/CT in order to evaluate disease extent, tumour metabolism and ER heterogeneity. We used time-to-event analyses (Kaplan-Meier and Cox proportional-hazards methods) to estimate progression-free (PFS) and overall survival (OS), in order to assess the independent prognostic value of [18F]FES PET/CT and [18F]FDG PET/CT, alone and in combination.

RESULTS

According to our criteria, we enrolled 49 patients. Over a median follow-up of 44.7 months, 35 patients suffered disease progression (71.4 %) and 15 died of disease (30.6 %). When the risk of disease progression was calculated by means of the Cox model, only [18F]FDG WB-B-MB was independently and directly associated to PFS (p = 0.02). On analysing the association between all prognostic parameters and survival, the Cox model showed that the only parameter associated with OS was the WB-B-MB FES/FDG ratio (p = 0.01).

CONCLUSION

The combined use of [18F]FES-PET/CT and [18F]FDG-PET/CT can identify ER heterogeneity in BC bone metastases. This heterogeneity is significantly associated with survival. Moreover, the extension of the FDG-avid component correlates with the risk of disease progression.

Heterogeneity in Signaling Pathway Activity within Primary and between Primary and Metastatic Breast Cancer

Targeted therapy aims to block tumor-driving signaling pathways and is generally based on analysis of one primary tumor (PT) biopsy. Tumor heterogeneity within PT and between PT and metastatic breast lesions may, however, impact the effect of a chosen therapy. Whereas studies are available that investigate genetic heterogeneity, we present results on phenotypic heterogeneity by analyzing the variation in the functional activity of signal transduction pathways, using an earlier developed platform to measure such activity from mRNA measurements of pathways' direct target genes. Statistical analysis comparing macro-scale variation in pathway activity on up to five spatially distributed PT tissue blocks (n = 35), to micro-scale variation in activity on four adjacent samples of a single PT tissue block (n = 17), showed that macro-scale variation was not larger than micro-scale variation, except possibly for the PI3K pathway. Simulations using a "checkerboard clone-size" model showed that multiple small clones could explain the higher micro-scale variation in activity found for the TGFβ and Hedgehog pathways, and that intermediate/large clones could explain the possibly higher macro-scale variation of the PI3K pathway. While within PT, pathway activities presented a highly positive correlation, correlations weakened between PT and lymph node metastases (n = 9), becoming even worse for PT and distant metastases (n = 9), including a negative correlation for the ER pathway. While analysis of multiple sub-samples of a single biopsy may be sufficient to predict PT response to targeted therapies, metastatic breast cancer treatment prediction requires analysis of metastatic biopsies. Our findings on phenotypic intra-tumor heterogeneity are compatible with emerging ideas on a Big Bang type of cancer evolution in which macro-scale heterogeneity appears not dominant.

Detection of Dural Metastases Before the Onset of Clinical Symptoms by 16α-[18F]Fluoro-17β-Estradiol PET in a Patient With Estrogen Receptor-Positive Breast Cancer

ABSTRACT

We offer an illustrative case about estrogen receptor (ER) imaging (also known as 16α-[18F]fluoro-17β-estradiol ([18F]-FES) PET) and the detection of metastatic lesions in the dural region. We present a case of a woman with ER-positive metastatic breast cancer and high [18F]-FES uptake in the dural region on PET imaging, without associated clinical symptoms. These lesions were missed on [18F]-FDG PET because of physiological [18F]-FDG uptake in the brain. This case highlighted some difficulties in the interpretation of imaging of brain metastases and demonstrated the added value of [18F]-FES PET imaging. [18F]-FES PET could be used to prove the presence of ER-positive metastases in the brain.

The quest for improving the management of breast cancer by functional imaging: The discovery and development of 16α-[18F]fluoroestradiol (FES), a PET radiotracer for the estrogen receptor, a historical review

INTRODUCTION

16α-[18F]Fluoroestradiol (FES), a PET radiotracer for the estrogen receptor (ER) in breast cancer, was the first receptor-targeted PET radiotracer for oncology and is continuing to prove its value in clinical research, antiestrogen development, and breast cancer care. The story of its conception, design, evaluation and use in clinical studies parallels the evolution of the whole field of receptor-targeted radiotracers, one greatly influenced by the research and intellectual contributions of William C. Eckelman.

METHODS AND RESULTS

The development of methods for efficient production of fluorine-18, for conversion of [18F]fluoride ion into chemically reactive form, and for its rapid and efficient incorporation into suitable estrogen precursor molecules at high molar activity, were all methodological underpinnings required for the preparation of FES. FES binds to ER with very high affinity, and its in vivo uptake by ER-dependent target tissues in animal models was efficient and selective, findings that preceded its use for PET imaging in patients with breast cancer.

ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE

Comparisons between ER levels measured by FES-PET imaging of breast tumors with tissue-specimen ER quantification by IHC and other methods show that imaging provided improved prediction of benefit from endocrine therapies. Serial imaging of ER by FES-PET, before and after dosing patients with antiestrogens, is used to determine the efficacious dose for established antiestrogens and to facilitate clinical development of new ER antagonists. Beyond FES imaging, PET-based hormone challenge tests, which evaluate the functional status of ER by monitoring rapid changes in tumor metabolic or transcriptional activity after a brief estrogen challenge, provide highly sensitive and selective predictions of whether or not there will be a favorable response to endocrine therapies. There is sufficient interest in the clinical applications of FES that FDA approval is being sought for its wider use in breast cancer.

CONCLUSIONS

FES was the first PET probe for a receptor in cancer, and its development and clinical applications in breast cancer parallel the conceptual evolution of the whole field of receptor-binding radiotracers.

Dual Tracers of 16α-[18F]fluoro-17β-Estradiol and [18F]fluorodeoxyglucose for Prediction of Progression-Free Survival After Fulvestrant Therapy in Patients With HR+/HER2- Metastatic Breast Cancer

Objective

The purpose of this study was to employ dual tracers 16α-[18F]fluoro-17β-estradiol (¹⁸F-FES) and [18F]fluorodeoxyglucose (¹⁸F-FDG) as imaging biomarkers in predicting progression-free survival (PFS) in ER-positive metastatic breast cancer (MBC) patients receiving fulvestrant therapy.

Methods

We retrospectively analyzed 35 HR+HER2- MBC patients who underwent ¹⁸F-FES and ¹⁸F-FDG PET/CT scans prior to fulvestrant therapy in our center. The SUVmax across all metastatic lesions on the PET/CT were assessed. The heterogeneity of ER expression was assigned by the presence of any ¹⁸F-FES negative lesions for patients with entirely ¹⁸F-FES positive lesions categorized into two groups by the median ratio of FES/FDG SUVmax, low FES/FDG, and high FES/FDG. PFS were estimated by the Kaplan-Meier method and compared by the log-rank test. Univariate and multivariate analyses were performed using the Cox proportional hazard model.

Results

In total, 12 patients had both ¹⁸F-FES negative and positive lesions, indicating the heterogeneity of ER expression in metastatic lesions. These patients had a low median PFS of 5.5 months (95% CI 2.3–8.7). Of patients with entirely ¹⁸F-FES positive lesions, 11 had a low FES/FDG, and 12 had a high FES/FDG. These groups had a median PFS of 29.4 months (95% CI 2.3–56.5) and 14.7 months (95% CI 10.9–18.5), respectively. The patients were stratified in three categories based on incorporating both ¹⁸F-FES and ¹⁸F-FDG imaging results that were significantly correlated with PFS by univariate analysis (P < 0.001) and multivariate analysis (P = 0.006).

Conclusion

¹⁸F-FES and ¹⁸F-FDG PET could serve as prognostic imaging biomarkers for ER-positive MBC patients treated with fulvestrant therapy.

Whole-Body Characterization of Estrogen Receptor Status in Metastatic Breast Cancer with 16α-18F-Fluoro-17β-Estradiol Positron Emission Tomography: Meta-Analysis and Recommendations for Integration into Clinical Applications

Estrogen receptor (ER) status by immunohistochemistry (IHC) of cancer tissue is currently used to direct endocrine therapy in breast cancer. Positron emission tomography (PET) with 16α-18F-fluoro-17β-estradiol (18 F-FES) noninvasively characterizes ER ligand-binding function of breast cancer lesions. Concordance of imaging and tissue assays should be established for 18 F-FES PET to be an alternative or complement to tissue biopsy for metastatic lesions. We conducted a meta-analysis of published results comparing 18 F-FES PET and tissue assays of ER status in patients with breast cancer. PubMed and EMBASE were searched for English-language manuscripts with at least 10 patients and low overall risk of bias. Thresholds for imaging and tissue classification could differ between studies but had to be clearly stated. We used hierarchical summary receiver-operating characteristic curve models for the meta-analysis. The primary analysis included 113 nonbreast lesions from 4 studies; an expanded analysis included 327 total lesions from 11 studies. Treating IHC results as the reference standard, sensitivity was 0.78 (95% confidence region 0.65-0.88) and specificity 0.98 (0.65-1.00) for the primary analysis of nonbreast lesions. In the expanded analysis including non-IHC tissue assays and all lesion sites, sensitivity was 0.81 (0.73-0.87) and specificity 0.86 (0.68-0.94). These results suggest that 18 F-FES PET is useful for characterization of ER status of metastatic breast cancer lesions. We also review current best practices for conducting 18 F-FES PET scans. This imaging assay has potential to improve clinically relevant outcomes for patients with (historically) ER-positive metastatic breast cancer, including those with brain metastases and/or lobular histology. IMPLICATIONS FOR PRACTICE: 16α-18F-fluoro-17β-estradiol positron emission tomography (18 F-FES PET) imaging assesses estrogen receptor status in breast cancer in vivo. This work reviews the sensitivity and specificity of 18 F-FES PET in a meta-analysis with reference tissue assays and discusses best practices for use of the tracer as an imaging biomarker. 18 F-FES PET could enhance breast cancer diagnosis and staging as well as aid in therapy selection for patients with metastatic disease. Tissue sampling limitations, intrapatient heterogeneity, and temporal changes in molecular markers make it likely that 18 F-FES PET will complement existing assays when clinically available in the near future.

Positron Emission Tomography-Based Response to Target and Immunotherapies in Oncology

2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) is a promising tool to support the evaluation of response to either target therapies or immunotherapy with immune checkpoint inhibitors both in clinical trials and, in selected patients, at the single patient's level. The present review aims to discuss available evidence related to the use of [18F]FDG PET (Positron Emission Tomography) to evaluate the response to target therapies and immune checkpoint inhibitors. Criteria proposed for the standardization of the definition of the PET-based response and complementary value with respect to morphological imaging are commented on. The use of PET-based assessment of the response through metabolic pathways other than glucose metabolism is also relevant in the framework of personalized cancer treatment. A brief discussion of the preliminary evidence for the use of non-FDG PET tracers in the evaluation of the response to new therapies is also provided.

PET Imaging Agents (FES, FFNP, and FDHT) for Estrogen, Androgen, and Progesterone Receptors to Improve Management of Breast and Prostate Cancers by Functional Imaging

Many breast and prostate cancers are driven by the action of steroid hormones on their cognate receptors in primary tumors and in metastases, and endocrine therapies that inhibit hormone production or block the action of these receptors provide clinical benefit to many but not all of these cancer patients. Because it is difficult to predict which individuals will be helped by endocrine therapies and which will not, positron emission tomography (PET) imaging of estrogen receptor (ER) and progesterone receptor (PgR) in breast cancer, and androgen receptor (AR) in prostate cancer can provide useful, often functional, information on the likelihood of endocrine therapy response in individual patients. This review covers our development of three PET imaging agents, 16α-[18F]fluoroestradiol (FES) for ER, 21-[18F]fluoro-furanyl-nor-progesterone (FFNP) for PgR, and 16β-[18F]fluoro-5α-dihydrotestosterone (FDHT) for AR, and the evolution of their clinical use. For these agents, the pathway from concept through development tracks with an emerging understanding of critical performance criteria that is needed for successful PET imaging of these low-abundance receptor targets. Progress in the ongoing evaluation of what they can add to the clinical management of breast and prostate cancers reflects our increased understanding of these diseases and of optimal strategies for predicting the success of clinical endocrine therapies.

Head-to-Head Evaluation of 18F-FES and 18F-FDG PET/CT in Metastatic Invasive Lobular Breast Cancer

Invasive lobular carcinoma (ILC) demonstrates lower conspicuity on ¹⁸F-FDG PET than the more common invasive ductal carcinoma. Other molecular imaging methods may be needed for evaluation of this malignancy. As ILC is nearly always (95%) estrogen receptor (ER)-positive, ER-targeting PET tracers such as 16α-¹⁸F-fluoroestradiol (¹⁸F-FES) may have value. We reviewed prospective trials at Memorial Sloan Kettering Cancer Center using ¹⁸F-FES PET/CT to evaluate metastatic ILC patients with synchronous ¹⁸F-FDG and ¹⁸F-FES PET/CT imaging, which allowed a head-to-head comparison of these 2 PET tracers. Methods: Six prospective clinical trials using ¹⁸F-FES PET/CT in patients with metastatic breast cancer were performed at Memorial Sloan Kettering Cancer Center from 2008 to 2019. These trials included 92 patients, of whom 14 (15%) were of ILC histology. Seven of 14 patients with ILC had ¹⁸F-FDG PET/CT performed within 5 wk of the research ¹⁸F-FES PET/CT and no intervening change in management. For these 7 patients, the ¹⁸F-FES and ¹⁸F-FDG PET/CT studies were analyzed to determine the total number of tracer-avid lesions, organ systems of involvement, and SUV_max of each organ system for both tracers. Results: In the 7 comparable pairs of scans, there were a total of 254 ¹⁸F-FES-avid lesions (SUV_max, 2.6-17.9) and 111 ¹⁸F-FDG-avid lesions (SUV_max, 3.3-9.9) suggestive of malignancy. For 5 of 7 (71%) ILC patients, ¹⁸F-FES PET/CT detected more metastatic lesions than ¹⁸F-FDG PET/CT. In the same 5 of 7 patients, the SUV_max of ¹⁸F-FES-avid lesions was greater than the SUV_max of ¹⁸F-FDG-avid lesions. One patient had ¹⁸F-FES-avid metastases with no corresponding ¹⁸F-FDG-avid metastases. There were no patients with ¹⁸F-FDG-avid distant metastases without ¹⁸F-FES-avid distant metastases, although in one patient liver metastases were evident on ¹⁸F-FDG but not on ¹⁸F-FES PET. Conclusion: ¹⁸F-FES PET/CT compared favorably with ¹⁸F-FDG PET/CT for detection of metastases in patients with metastatic ILC. Larger prospective trials of ¹⁸F-FES PET/CT in ILC should be considered to evaluate ER-targeted imaging for clinical value in patients with this histology of breast cancer.

Application of PET Tracers in Molecular Imaging for Breast Cancer

PURPOSE OF REVIEW

Molecular imaging with positron emission tomography (PET) is a powerful tool to visualize breast cancer characteristics. Nonetheless, implementation of PET imaging into cancer care is challenging, and essential steps have been outlined in the international "imaging biomarker roadmap." In this review, we identify hurdles and provide recommendations for implementation of PET biomarkers in breast cancer care, focusing on the PET tracers 2-[18F]-fluoro-2-deoxyglucose ([18F]-FDG), sodium [18F]-fluoride ([18F]-NaF), 16α-[18F]-fluoroestradiol ([18F]-FES), and [89Zr]-trastuzumab.

RECENT FINDINGS

Technical validity of [18F]-FDG, [18F]-NaF, and [18F]-FES is established and supported by international guidelines. However, support for clinical validity and utility is still pending for these PET tracers in breast cancer, due to variable endpoints and procedures in clinical studies. Assessment of clinical validity and utility is essential towards implementation; however, these steps are still lacking for PET biomarkers in breast cancer. This could be solved by adding PET biomarkers to randomized trials, development of imaging data warehouses, and harmonization of endpoints and procedures.

Visual and quantitative evaluation of [18F]FES and [18F]FDHT PET in patients with metastatic breast cancer: an interobserver variability study

Purpose

Correct identification of tumour receptor status is important for treatment decisions in breast cancer. [¹⁸F]FES PET and [¹⁸F]FDHT PET allow non-invasive assessment of the oestrogen (ER) and androgen receptor (AR) status of individual lesions within a patient. Despite standardised analysis techniques, interobserver variability can significantly affect the interpretation of PET results and thus clinical applicability. The purpose of this study was to determine visual and quantitative interobserver variability of [¹⁸F]FES PET and [¹⁸F]FDHT PET interpretation in patients with metastatic breast cancer.

Methods

In this prospective, two-centre study, patients with ER-positive metastatic breast cancer underwent both [¹⁸F]FES and [¹⁸F]FDHT PET/CT. In total, 120 lesions were identified in 10 patients with either conventional imaging (bone scan or lesions > 1 cm on high-resolution CT, n = 69) or only with [¹⁸F]FES and [¹⁸F]FDHT PET (n = 51). All lesions were scored visually and quantitatively by two independent observers. A visually PET-positive lesion was defined as uptake above background. For quantification, we used standardised uptake values (SUV): SUV_max, SUV_peak and SUV_mean.

Results

Visual analysis showed an absolute positive and negative interobserver agreement for [¹⁸F]FES PET of 84% and 83%, respectively (kappa = 0.67, 95% CI 0.48–0.87), and 49% and 74% for [¹⁸F]FDHT PET, respectively (kappa = 0.23, 95% CI − 0.04–0.49). Intraclass correlation coefficients (ICC) for quantification of SUV_max, SUV_peak and SUV_mean were 0.98 (95% CI 0.96–0.98), 0.97 (95% CI 0.96–0.98) and 0.89 (95% CI 0.83–0.92) for [¹⁸F]FES, and 0.78 (95% CI 0.66–0.85), 0.76 (95% CI 0.63–0.84) and 0.75 (95% CI 0.62–0.84) for [¹⁸F]FDHT, respectively.

Conclusion

Visual and quantitative evaluation of [¹⁸F]FES PET showed high interobserver agreement. These results support the use of [¹⁸F]FES PET in clinical practice. In contrast, visual agreement for [¹⁸F]FDHT PET was relatively low due to low tumour-background ratios, but quantitative agreement was good. This underscores the relevance of quantitative analysis of [¹⁸F]FDHT PET in breast cancer.

Trial registration

ClinicalTrials.gov, NCT01988324. Registered 20 November 2013, https://clinicaltrials.gov/ct2/show/NCT01988324?term=FDHT+PET&draw=1&rank=2.

Molecular imaging to identify patients with metastatic breast cancer who benefit from endocrine treatment combined with cyclin-dependent kinase inhibition

BACKGROUND

Adding cyclin-dependent kinase (CDK) inhibitor to endocrine treatment improves outcome in œstrogen receptor (ER) positive metastatic breast cancer, but identifying the subset of patients who benefit is challenging. Response is potentially associated with ER expression heterogeneity. This is because, unlike the primary tumour in the breast that is localized to the organ, the metastatic breast cancer has spread and continues to spread to distant locations in the body such as bones, lungs, liver, axial skeleton, even to the central nervous system like the brain, wherefrom obtaining biopsies are not easy, and also, the metastasised tissues are heterogeneous. Positron emission tomography (PET) with 16α-[¹⁸F]fluoro-17β-œstradiol (FES), briefly referred to as FES-PET, allows whole-body ER assessment. We explored whether FES-PET heterogeneity and FES uptake were related to letrozole and palbociclib outcome, in patients with ER positive, metastatic breast cancer.

PATIENTS AND METHODS

Patients underwent a baseline FES-PET and ¹⁸F-fluorodeoxyglucose (FDG) PET, the FDG-PET served to help identify active sites of breast cancer with contrast-enhanced computed tomography (CT). FES-PET heterogeneity score (% FES positive lesions divided by all lesions on FDG-PET and/or CT) and FES uptake were related to outcome and 8-week FDG-PET response. Circulating tumour DNA (CtDNA) samples for ESR1 mutation analysis were collected at baseline.

RESULTS

In 30 patients with 864 metastatic lesions, baseline FES-PET heterogeneity was assessed. In 27 patients with 688 lesions, response was evaluated. Median time to progression (TTP) was 73 weeks (95% confidence interval [CI] 21 to ∞) in 7 patients with 100% FES positive disease, 27 weeks (14-49) in heterogeneous FES positive disease (20 patients), and 15 weeks (9 to ∞) without FES positivity (three patients; log-rank P = 0.30). Geometric mean FES uptake was 2.3 for metabolic progressive patients, 2.5 (P_{vs progression} = 0.82) for metabolic stable disease, and 3.3 (P_{vs progression} = 0.40) for metabolic response (P_trend = 0.21). ESR1 mutations, found in 13/23 patients, were unrelated to FES uptake.

CONCLUSION

This exploratory study suggests that FES-PET heterogeneity may potentially identify the subset of ER positive, metastatic breast cancer patients who benefit from letrozole combined with CDK inhibition.

CLINICAL TRIAL INFORMATION

NCT02806050.

Recent Advances in Imaging Steroid Hormone Receptors in Breast Cancer

Estrogen receptor (ER) and progesterone receptor (PR) are important prognostic and predictive biomarkers in breast cancer. PET using ER- and PR-specific radioligands enables a whole-body, noninvasive assessment of receptor expression. Recent investigations of ER imaging with ¹⁸F-fluoroestradiol have focused on diagnosing ER-positive metastatic disease, optimizing ER-targeted drug dosage, and predicting endocrine therapy benefit. Studies of PR imaging with ¹⁸F-fluorofuranyl norprogesterone have investigated how imaging changes in PR expression as a downstream target of ER activation may reflect an early response to ER-targeted therapy. This focused review highlights recent achievements in preclinical and clinical imaging of ER and PR in breast cancer.

CDK4/6 inhibition in low burden and extensive metastatic breast cancer: summary of an ESMO Open-Cancer Horizons pro and con discussion

In December 2017, ESMO Open-Cancer Horizons convened a round-table discussion on the background and latest data regarding cyclin-dependent kinase (CDK)4/6 inhibitors with endocrine therapy (ET) in the treatment of endocrine-sensitive breast cancer (BC). A review on this discussion was published in summer 2018 (https://esmoopen.bmj.com/content/3/5/e000368).Endocrine-sensitive BC with non-visceral disease and limited spread of the metastases.Endocrine-sensitive BC with non-life-threatening visceral involvement. Several open questions were identified, which led to a second ESMO Open discussion on CDK4/6 inhibitors, taking place in December 2018 and covered in this article. The panel discussed two important clinical scenarios and the pro and cons of a treatment approach with CDK4/6 inhibitors for each scenario:Endocrine-sensitive BC with non-visceral disease and limited spread of the metastases.Endocrine-sensitive BC with non-life-threatening visceral involvement. Regarding scenario 1, the panel agreed that CDK4/6 inhibitors should be recommended in first-line therapy for most patients if cost and practicality allow. However, the use of single-agent ET with an aromatase inhibitor in the first-line treatment of these patients is still a possibility for a small group of patients with very limited disease, such as one or two bone lesions or limited lymph node involvement. Regarding scenario 2, chemotherapy is the first approach for patients with endocrine-sensitive metastatic BC with life-threatening visceral involvement because of the need for a faster response. The therapeutic approaches for patients with non-life-threatening visceral involvement are still under debate. Nevertheless, CDK4/6 inhibitors are currently the treatment of choice for most patients with a close follow-up of tumour response. A treatment algorithm has been suggested at the round table.

Integrating molecular nuclear imaging in clinical research to improve anticancer therapy

Effective patient selection before or early during treatment is important to increasing the therapeutic benefits of anticancer treatments. This selection process is often predicated on biomarkers, predominantly biospecimen biomarkers derived from blood or tumour tissue; however, such biomarkers provide limited information about the true extent of disease or about the characteristics of different, potentially heterogeneous tumours present in an individual patient. Molecular imaging can also produce quantitative outputs; such imaging biomarkers can help to fill these knowledge gaps by providing complementary information on tumour characteristics, including heterogeneity and the microenvironment, as well as on pharmacokinetic parameters, drug-target engagement and responses to treatment. This integrative approach could therefore streamline biomarker and drug development, although a range of issues need to be overcome in order to enable a broader use of molecular imaging in clinical trials. In this Perspective article, we outline the multistage process of developing novel molecular imaging biomarkers. We discuss the challenges that have restricted the use of molecular imaging in clinical oncology research to date and outline future opportunities in this area.

18F-Fluoroestradiol PET Imaging of Activating Estrogen Receptor-α Mutations in Breast Cancer

The purpose of this study was to determine the effect of estrogen receptor-α gene (ESR1) mutations at the tyrosine (Y) 537 amino acid residue within the ligand binding domain on ¹⁸F-fluoroestradiol (¹⁸F-FES) binding and in vivo tumor uptake compared with wild-type (WT)-estrogen receptor α (ER). Methods: ER-negative MDA-MB-231 breast cancer cells were used to generate stable cell lines that express WT-ER, Y537S, or Y537C mutant ER. Receptor expression and localization were confirmed by Western blot and immunofluorescence, respectively. ER transcriptional function was measured using an estrogen response element-luciferase reporter gene assay and quantitative polymerase chain reaction analysis of ER-regulated endogenous target genes. Saturation binding and competition assays were performed to determine equilibrium dissociation constant (K_d) and half maximal inhibitory concentration (IC50) values. ¹⁸F-FES uptake was measured in tumor xenografts grown in female athymic nude mice by small-animal PET/CT imaging and tissue biodistribution using 5.55 MBq (150 μCi) of ¹⁸F-FES. A 10-fold-lower injected dose of 0.555 MBq (15 μCi) of ¹⁸F-FES was also used for tissue biodistribution. Statistical significance was determined using ANOVA. Results: Y537S and Y537C mutations resulted in increased ER transcriptional activity in the absence of estrogen compared with WT-ER (11.48 ± 2.42 fold; P = 0.0002, and 5.89 ± 0.94 fold; P = 0.04, respectively). Constitutive ER activation of two target genes (PGR and TFF1) in the absence of estrogen was also observed in Y537S- and Y537C-ER cells compared with WT-ER. K_d values for ¹⁸F-FES were 0.98 ± 0.54 nM for Y537S-ER (P = 0.27) and 0.24 ± 0.03 nM for Y537C-ER (P = 0.95) compared with 0.07 ± 0.03 nM for WT-ER. IC50 values were 0.22 ± 0.09 nM for Y537S-ER (P = 0.97), 0.18 ± 0.09 nM for Y537C-ER (P = 0.99), and 0.19 ± 0.11 nM for WT-ER. Tumor xenografts expressing Y537S-ER (mean percentage injected dose per gram, 1.45 ± 0.06; P = 0.77) and Y537C-ER (2.09 ± 0.20; P = 0.21) had similar ¹⁸F-FES uptake compared with WT-ER (1.68 ± 0.12). Comparable ¹⁸F-FES uptake between Y537S-, Y537C-, and WT-ER xenografts was also observed using a 10-fold-lower injected dose with the tissue biodistribution assay. Conclusion: Since tumoral uptake of ¹⁸F-FES is not significantly impacted by Y537S-ER or Y537C-ER mutations, the potential diagnostic utility of ¹⁸F-FES PET imaging is expected to be equally valid for patients with or without these activating ESR1 mutations.